Method and arrangement for signaling of parameters in a wireless network

ABSTRACT

A mobile terminal receives, over a first cell configured on a carrier frequency, at least one parameter associated with a second cell configured on a carrier frequency. The at least one parameter comprises a cell identity. The mobile terminal then derives at least one physical layer characteristic for the second cell based on the received at least one parameter. Thereby, the mobile terminal is able to receive transmissions over the second cell, even if it could not initially detect the presence of the cell.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/792,218, filed Jul. 6, 2015, which was a continuation of U.S.application Ser. No. 13/061,243, filed Feb. 28, 2011, now U.S. Pat. No.9,106,380, which was the National Stage of International Application No.PCT/SE2010/051055, filed Oct. 1, 2010, which claims the benefit of U.S.Provisional Application 61/356,726, filed Jun. 21, 2010, the disclosuresof each of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present application relates to signaling techniques between awireless mobile station and a network node in a wireless communicationssystem. In particular, it relates to signaling of cell identityinformation in a wireless communications network.

BACKGROUND

The Long-Term Evolution (LTE) wireless communication system specified bythe 3rd-Generation Partnership Project (3GPP) uses orthogonalfrequency-division multiplexing (OFDM) in the downlink anddiscrete-Fourier-transform-spread OFDM in the uplink. The basic LTEdownlink physical resource can thus be seen as a time-frequency grid.This is illustrated in FIG. 1, where each resource element correspondsto one OFDM subcarrier during one OFDM symbol interval.

In the time domain, LTE downlink transmissions are organized into radioframes of 10 milliseconds, each radio frame consisting of tenequally-sized subframes of length T_(subframe)=1 millisecond. The LTEframe structure is illustrated in FIG. 2.

Furthermore, the resource allocation in LTE is typically described interms of resource blocks, where a resource block corresponds to one slot(0.5 milliseconds) in the time domain and 12 contiguous subcarriers inthe frequency domain. Resource blocks are numbered in the frequencydomain, starting with 0 from one end of the system bandwidth.

Earlier versions of the LTE standard, e.g. Release 8 and 9, supportbandwidths up to 20 MHz. However, in order to meet the IMT-Advancedrequirements, 3GPP has initiated work on LTE Release 10. One of thegoals of LTE Release 10 is to support bandwidths larger than 20 MHz.However, one important requirement on LTE Release 10 is to assurebackward compatibility with earlier versions of the standard. Thisbackwards compatibility should also include spectrum compatibility. As aresult, a LTE Release 10 carrier wider than 20 MHz should appear as anumber of distinct LTE carriers to a legacy terminal, e.g. an LTERelease 8 or Release 9 terminal. Each such carrier can be referred to asa Component Carrier.

In particular for early LTE Release 10 deployments, it can be expectedthat there will be a smaller number of LTE Release 10-capable terminalscompared to many LTE legacy terminals. Therefore, it is necessary toassure an efficient use of a wide carrier also for legacy terminals,i.e., that it is possible to implement carriers in such a manner thatlegacy terminals can be scheduled in all parts of the wideband LTERelease 10 carrier. The most straightforward way to obtain this would beby means of “carrier aggregation.” Carrier aggregation implies that anLTE Release 10 terminal can receive multiple component carriers, wherethe component carriers have, or at least have the possibility to have,the same structure as a Release 8 carrier. The same structure as Release8 implies that all Release 8 signals, e.g. primary and secondarysynchronization signals, reference signals, and system information aretransmitted on each carrier. Carrier aggregation is illustratedgenerally in FIG. 3.

During initial access, a carrier-aggregation capable terminal, e.g. aLTE Release 10 terminal, behaves similarly to a legacy terminal. Uponsuccessful connection to the network, via a first carrier, a terminalmay—depending on its own capabilities and the network—be configured withadditional component carriers in the uplink and/or downlink.Configuration of these carriers is based on Radio Resource Control(RRC). Due to the heavy signaling and rather slow speed of RRCsignaling, it is envisioned that a terminal may often be configured withmultiple component carriers even though not all of them are used at agiven instant. If a terminal is configured on multiple componentcarriers this implies it has to monitor all downlink component carriersfor the corresponding Physical Downlink Control Channel (PDCCH) andPhysical Downlink Shared Channel (PDSCH). This implies that a widerreceiver bandwidth, higher sampling rates, etc., must generally beactive, resulting in high power consumption for the mobile terminal.

To mitigate these problems, LTE Rel-10 supports a component carrieractivation procedure, in addition to the configuration procedures.Accordingly, the terminal monitors only configured and activatedcomponent carriers for PDCCH and PDSCH. Since activation of componentcarriers is based on Medium Access Control (MAC) control elements—whichare faster than RRC signaling—activation/de-activation can follow thenumber of component carriers that is required to fulfil the current datarate needs. Upon arrival of large data amounts, multiple componentcarriers are activated, used for data transmission, and thende-activated if not needed anymore. All but one component carrier, thedownlink Primary component carrier (DL PCC), can be de-activated. Notethat the PCC is not necessarily the same for all terminals in the cell,i.e. different terminals may be configured with different Primarycomponent carriers. Activation therefore provides the possibility toconfigure multiple component carriers but only activate them on anas-needed basis. Most of the time a terminal would have one or very fewcomponent carriers activated, resulting in a lower reception bandwidthand thus lower battery consumption.

Scheduling of a component carrier is done on the PDCCH via downlinkassignments. Control information on the PDCCH is formatted as a DownlinkControl Information (DCI) message. In Release 8, a terminal onlyoperates with one downlink and one uplink component carrier. As aresult, the associations between downlink assignment, uplink grants andthe corresponding downlinks and uplinks component carriers are clear. InRelease 10, however, two modes of carrier aggregation need to bedistinguished. The first case is very similar to the operation ofmultiple Release 8 or 9 terminals. In this mode a downlink assignment oruplink grant contained in a DCI message transmitted on a componentcarrier is either valid for the downlink component carrier itself or fora corresponding uplink component carrier. The association of uplink anddownlink component carriers with one another can be cell-specific orUE-specific linking. In a second mode of operation, a DCI message isaugmented with an indicator that specifies a component carrier, theCarrier Indicator Field (CIF). A DCI containing a downlink assignmentwith CIF is valid for the downlink component carrier indicated with theCIF. Likewise, a DCI containing an uplink grant with CIF is valid forthe indicated uplink component carrier. This is referred to ascross-carrier scheduling.

It should be noted that the inventive techniques disclosed herein arenot restricted to the particular terminology used here. It also shouldbe noted that during the development of the standards for carrieraggregation in LTE, various terms have been used to describe, forexample, component carriers. Those skilled in the art will appreciate,then, that the techniques of the present disclosure are thereforeapplicable to systems and situations where terms like multi-cell ordual-cell operation are used. In this disclosure, the term “primaryserving cell” or “PCell” refers to a cell configured on a primarycomponent carrier, PCC. A user equipment which is capable of carrieraggregation may, in addition to the PCell, also aggregate one or moresecondary serving cells, “SCells”. The SCells are cells configured onsecondary component carriers, SCCs. Note that “cell” in this contextrefers to a network object, whereas “component carrier” or “carrier”refers to the physical resource, i.e. frequency band, that the cell isconfigured to use.

In the subsequent discussions, a basic heterogeneous network deploymentscenario with two cell layers, here referred to as “macro layer” and“pico layer”, respectively, is assumed. No specific assumptions are maderegarding the characteristics of the different layers except that theycorrespond to cells of substantially different size of their respectivecoverage area, fundamentally defined by the coverage area of the basiccontrol signals/channels, such as Primary Synchronization Channel,(PSS), Secondary Synchronization Channel (SSS), Physical BroadcastChannel (PBCH), Cell Specific Reference Signals (CRS), PDCCH, etc.Especially, what is referred to herein as a “pico layer” can be a microlayer, a conventional outdoor or indoor pico layer, a layer consistingof relays, or a Home e-Node B (HeNB) layer.

Various inter-cell interference scenarios can be anticipated forco-channel heterogeneous network deployments. FIG. 4 illustrates threescenarios that may cause severe interference. Cases (a) and (b) involvean HeNB operating in Closed Subscriber Group (CSG) mode. In the CSGmode, access to the HeNB is granted only to those subscribers that aremembers of a Closed Subscriber Group associated with the HeNB. Theleft-hand side of FIG. 4 illustrates how a HeNB in a femto cell causesinterference towards a macro cell user that has no access to the femtocell (case (a)), and how a macro cell edge user with no access to aparticular femto cell may cause interference towards the HeNB (case(b)). Inter-cell interference is indicated by the dotted arrows.

The right-hand side of FIG. 4, case (c), illustrates how theinterference from a macro evolved-Node B (eNB) towards a pico or femtocell edge user increases, up to Δ, if path-loss-based serving-cellselection is used instead of selection based on the strongest receiveddownlink signal. The solid and dotted lines illustrate Rx power, and thedashed lines show 1/pathloss. To understand why this increase ininterference occurs, assume that the user equipment is in closeproximity to the pico base station, but far away from the macro eNB. Ifthe UE performs path-loss based cell selection the foot print of thepico eNB increases, i.e. the UE connects to the pico eNB whereotherwise, using received signal power-based cell selection, it wouldhave connected to the macro eNB since the received power is stronger.This implies that interfering signals from the macro eNB are strongerthan desired signals from the pico eNB. On the uplink, however, thesituation improves since the UE connects to that eNB to which it seesthe lowest pathloss and thus the received power at the eNB is maximized.

The worst inter-cell interference issue in co-channel heterogeneousnetwork deployments in LTE arise with respect to resources that cannotbenefit from inter-cell interference coordination (ICIC). Forschedulable data transmissions, such as PDSCH and Physical Uplink SharedChannel (PUSCH), inter-cell interference can be mitigated throughinter-cell coordination, such as by via soft or hard physical resourcepartitioning. Coordination information can be exchanged acrosslayers/cells via λ2 interfaces, the standard interfaces between LTEradio base stations (eNBs). However, ICIC is not possible for signalsthat need to be transmitted on specific resources, e.g. parts of systeminformation.

It is desirable that legacy mobile terminals (user equipments, or UEs,in 3GPP terminology) can operate and benefit from heterogeneous networkdeployments, such as by accessing any available pico layers to improveuplink performance, even when the received signal power from the macrolayer is significantly higher. Such cell selection can be achieved, forexample, by use of an offset applied to Reference Signal Received Power(RSRP) measurements carried out by the UE (corresponding to Δ in FIG.4). The current specification allows for an offset up to 24 dB, whichshould be sufficient for most heterogeneous network scenarios.

To mitigate severe downlink inter-cell interference from macro eNBstowards control regions of pico subframes, operating layers on differentcarriers appears to be the only option to ensure robust communicationsfor legacy mobile terminals in heterogeneous network deployments. Thisimplies that the whole system bandwidth will not always be available forlegacy mobile terminals and may result in reduced user throughputs. Oneexample of reduced throughput would be a split of a contiguous systembandwidth of 20 MHz into two carries, e.g. 10 MHz bandwidth on eachcarrier.

As pointed out above, operating different layers on differentnon-overlapping carrier frequencies may lead to resource-utilizationinefficiency. With the heterogeneous network illustration depicted inFIG. 5, this would imply that the overall available spectrum consists oftwo carriers f1 and f2, with f1 and f2 being exclusively used in themacro and pico layers, respectively. In the subsequent discussions, itis assumed that the layers are synchronized with time aligned eNBtransmissions and that f1 and f2 have non-overlapping frequency bands.

In many cases it can be assumed that the pico layer is deployed to carrythe main part of the traffic, and especially, to provide the highestdata rates, while the macro layer provides full-area coverage, i.e., tofill any coverage holes within the pico layer. In such a case, it isdesirable that the full bandwidth, corresponding to carriers f1 and f2,is available for data transmission within the pico layer. One can alsoenvision cases when it is desirable, that the full bandwidth (f1 and f2)is available for data transmission also within the macro layer.

As already mentioned, sharing of the resources, i.e. operation on thesame set of carriers, between the cell layers for data transmission canbe accomplished by means of Inter-Cell Interference Coordination (ICIC)methods that can be more or less dynamic depending on the coordinationcapabilities between the layers, and their constituent radio basestations. However, interference concerns remain with respect to thetransmission of signals and/or channels that cannot rely on traditionalICIC methods but need to be transmitted on specific, well-defined,resources. In LTE, these include, for example, the synchronizationsignals (PSS/SSS), the Physical Broadcast Channel (PBCH), and thelayer1/layer 2 (L1/L2) control channels (PDCCH, PCFICH and PHICH).

Clearly, all these signals must be transmitted on at least one downlinkcarrier within each cell layer, as they are needed to enable a userequipment to detect, and connect to the cell. The downlink carrier onwhich these signals are always transmitted will be referred to as theprimary carrier, or primary component carrier (PCC) in the followingdisclosure. It should be noted, however, that these signals may also betransmitted on one or more secondary component carriers, SCCs, and ifthis is the case, a user equipment may receive the signals either fromthe PCC, or from an SCC.

For the purposes of discussion, assume that the primary carrier, PCC,corresponds to carrier f1 in the macro layer and carrier f2 in the picolayer.

For the downlink situation, the three cases shown in FIG. 6 areconsidered below, where Case 1 differ from Case 2 with respect to theuse of an Open Subscriber Group (OSG) in the former. In Case 3, bothcarriers, f1 and f2, are available also at the macro layer.

In Case 1, it is assumed that Carrier f1, which is the macro primarycomponent carrier, or PCC, should be available for PDSCH transmission,i.e. traffic data transmission, also within the pico layer. It isassumed that a mobile terminal only accesses the macro layer when thepath loss to the macro layer is of the same order or smaller, comparedto the path loss to the pico layer.

In this case, the basic downlink control signals/channels above can betransmitted on f1 also in the pico layer with no severe interference tomobile terminals accessing the macro layer. Thus both f1 and f2 can bedeployed as “normal”, release 8 compatible, carriers in the pico layer.However, a legacy mobile terminal would only be able to access f1 closeto the pico cell site where the path loss to the pico cell is muchsmaller than the path-loss to the macro cell, in order to avoid strongcontrol-channel interference from the macro cell. Closer to thepico-cell border of the pico cell, carrier-aggregation capable UEs, e.g.Release 10 mobile terminals, would need to access on carrier f2, toavoid strong interference to PSS/SSS and PBCH from the macro cell.However, these mobile terminals could be scheduled PDSCH transmissionson f1, using cross-carrier scheduling signaled via the PDCCH on f2. Notethat, to avoid interference from cell-specific reference signals (CRS)for the macro layer, pico-cell PDSCH transmission on f1 must rely onUE-specific reference signals (RS) for channel estimation, at least whenthe UE is close to the pico-cell border. This is because CRS aretypically transmitted on specific resources in the data region of asubframe, so that the CRS transmitted on f1 in the macro cell willcollide with the CRS transmitted on f1 in the pico cell. One mightconsider using frequency shifts of CRS across layers, but the macro CRSwould then cause interference towards data resource elements of thepico.

In case 2, similarly to case 1, carrier f1 should be available for PDSCHtransmission also within the pico layer. However, a mobile terminalshould be able to access the macro cell even when close to the picocell. This scenario may occur when the pico layer consists of HeNBsbelonging to Closed Subscriber Groups (CSGs), and when a mobile terminalnot belonging to the CSG approaches a HeNB. The mobile terminal will notbe allowed access to the HeNB, and must therefore connect to the macrocell instead. In this case, the pico layer must not transmit thechannels above (PSS/SSS, PBCH, CRS, PDCCH, etc.) on f1, in order toavoid interference to the mobile terminals that are accessing the macrolayer in the vicinity of a pico site. Rather, the corresponding resourceelements should be empty, i.e. muted. Thus, legacy mobile terminals canonly access the pico layer on f2 while Release 10 mobile terminals canbe scheduled on both f1 and f2, in the same way as for case 1.

In Case 3, in addition to carrier f1 being available for PDSCHtransmission within the pico layer, carrier f2 should be available forPDSCH transmission within the macro layer.

In this case, the macro layer must not transmit the basic downlinksignals/channels above (PSS/SSS, PBCH, CRS, PDCCH, etc.) on f2, in orderto avoid interference to mobile terminals that are accessing the picolayer and that may be in a location where signals from the macro layerare received with much higher power, even though the path loss to thepico layer is substantially smaller. Rather, as with case 2, thecorresponding resource elements should be empty, i.e. muted. Thus,legacy mobile terminals can only access the macro layer on f1 whilecarrier-aggregation capable terminals, e.g. Release 10 mobile terminals,can be scheduled in the macro layer on both f1 and f2. It should benoted that a mobile terminal operating in this scenario can only bescheduled on the macro layer on f2 in such a way that it does not causeany severe interference to the pico cell, either by ensuring that thereis no mobile terminal being scheduled on the corresponding resource inany pico cell under the coverage area of the macro cell, or by using lowpower for the macro-cell transmission, where possible.

Note that in the case where all pico cells are relatively far from themacro-cell site, one could transmit also the basic controlsignals/channels with reduced power on f2 from the macro-cell site.However, this would make the macro-cell on f2 appear as a separate picocell, located at the same point as the macro cell on f1.

In LTE, the mobile terminals derive the physical cell ID for a cell fromthe synchronization signals PSS/SSS. Likewise, the number of transmitantenna ports is blindly derived from the CRC scrambling code of thePBCH. As a result, if signals are only transmitted with zero or reducedpower on a secondary component carrier, i.e. in an SCell, the UE isunable to determine either the physical cell ID or the number oftransmit antenna ports. The same problem may occur even if the signalsare not muted, for instance if a UE is in the vicinity of a pico cellwhich is interfered by a macro cell transmitting with high power on thesame carrier. In this case, the UE may not be able to hear and/or decodethe synchronization signals from the pico cell due to the severeinterference.

In LTE, the physical cell ID is used to derive uplink demodulationreference signals (DMRS), sounding reference signals (SRS), physicaluplink shared channel (PUSCH) scrambling, PDSCH scrambling, physicaluplink control channel (PUCCH) signaling, L1/L2 control signaling,reference signals (RS) for transmissions using Multi-Media Broadcastover a Single Frequency Network, etc. Likewise, the number of transmitantenna ports is needed by the mobile terminal in LTE, as it influencesthe CRS, layer mapping, precoding, L1/L2 control signaling, etc. TheCRS, in particular, are needed to perform mobility measurements, ifconfigured on a secondary component carrier.

Thus, if a UE is not able to receive the necessary control andsynchronization signals from a cell, it will not be able to detect thatcell or establish communication with it, e.g. to perform carrieraggregation, or perform mobility measurements. This may lead to reducedperformance. If the UE is not able to aggregate a secondary carrierbecause it can't detect the SCell, the UE may not be able to use itsfull bandwidth capacity, leading to lower throughput. If the UE is notable to receive reference signals and perform mobility measurements on aneighboring cell, the UE may end up being served by a less-than-optimalcell, which will reduce performance.

SUMMARY

It is therefore an object of the present disclosure to providemechanisms for improving performance and resource utilization inwireless networks.

As detailed further below, some embodiments set forth in this disclosuredescribe techniques to enable signaling of physical cell ID and numberof transmit antenna ports for another component carrier on a componentcarrier. In particular, some embodiments relate to methods applicable ina system consisting of at least two cells, wherein information regardingthe cell identity, or the number of transmit antenna ports, or both, istransmitted over a second cell signal.

Various embodiments in which this solution is embodied in the radio basestation and the information is conveyed and transmitted from theradio-base-station are provided. These embodiments include solutionswherein the radio base station provides the aforementioned informationby means of dedicated signaling, i.e., it is provided to specific mobileterminals with messages intended for each UE separately. In otherembodiments, the information may be provided by broadcasting, such thatthe information may be simultaneously received by multiple userequipments.

Corresponding receiver methods in the mobile terminals are also coveredby the present disclosure.

In some embodiments, a method in a user equipment is provided. The userequipment receives, over a first cell configured on a carrier frequency,at least one parameter associated with a second cell configured on acarrier frequency. The at least one parameter comprises a cell identity.The user equipment then derives at least one physical layercharacteristic for the second cell based on the received at least oneparameter, thereby enabling the user equipment to receive transmissionsover the second cell.

In some embodiments, a method in a network node is provided. The networknode serves a first cell configured on a carrier frequency. The networknode transmits, over the first cell, at least one parameter associatedwith a second cell configured on a carrier frequency. The at least oneparameter comprises a cell identity. The network node also transmits anindication to use the at least one parameter to derive at least onephysical layer characteristic for the second cell.

In some embodiments, a user equipment is provided, comprising atransceiver and one or more processing circuits. The processing circuitsare configured to receive, over a first cell configured on a carrierfrequency, at least one parameter associated with a second cellconfigured on a carrier frequency. The at least one parameter comprisesa cell identity. The processing circuits are further configured toderive at least one physical layer characteristic for the second cellbased on the received at least one parameter, thereby enabling the userequipment to receive transmissions over the second cell.

In some embodiments, a network node is provided, comprising atransceiver and one or more processing circuits. The processing circuitsare configured to transmit, over a first cell configured on a carrierfrequency, at least one parameter associated with a second cellconfigured on a carrier frequency, wherein the at least one parametercomprises a cell identity. The processing circuits are furtherconfigured to transmit an indication to use the at least one parameterto derive at least one physical layer characteristic for the secondcell.

By transmitting parameters associated with a second cell over a firstcell, it is made possible for a user equipment to acquire theseparameters, and use them to derive necessary physical layercharacteristics for the first cell, even if the user equipment is notable to detect control and/or synchronization signals in the secondcell. Once the physical layer characteristics have been derived, theuser equipment may receive transmissions in the second cell, forinstance to perform measurements, or to use the second cell as an SCell.

Thus, an advantage of some embodiments is that a user equipment may gainaccess to additional resources, thereby increasing the bandwidthavailable to the user equipment.

A further advantage of some embodiments is that throughput and/orchannel quality may be improved, as the user equipment is able toperform measurements and possibly be handed over to a better cell, whichit could not otherwise have detected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the LTE downlink physicalresource.

FIG. 2 is a schematic diagram illustrating the LTE time-domainstructure.

FIG. 3 is a schematic diagram illustrating Carrier Aggregation.

FIG. 4 is a schematic diagram illustrating inter-cell interferencescenarios.

FIG. 5 is a schematic diagram illustrating frequency separation betweendifferent layers in a heterogeneous network.

FIG. 6 is a schematic diagram illustrating different deployment optionsfor heterogeneous networks.

FIG. 7 is a schematic diagram illustrating muting in a heterogeneousnetwork.

FIG. 8 is a schematic diagram illustrating inter-cell interferencecoordination (ICIC).

FIG. 9 is a schematic diagram illustrating a wireless communicationsnetwork according to an embodiment.

FIG. 10 is a flow chart illustrating a method according to anembodiment.

FIG. 11 is a flow chart illustrating a method according to anembodiment.

FIG. 12 is a schematic diagram illustrating a wireless communicationsnetwork according to an embodiment.

FIG. 13 is a flow chart illustrating a method according to anembodiment.

FIG. 14 is a flow chart illustrating a method according to anembodiment.

FIG. 15 is a flow chart illustrating a method according to anembodiment.

FIG. 16 is a flow chart illustrating a method according to anembodiment.

FIG. 17 is a flow chart illustrating a method according to anembodiment.

FIG. 18 is a block diagram illustrating a user equipment according to anembodiment.

FIG. 19 is a block diagram illustrating a network node according to anembodiment.

ABBREVIATIONS

CC Component Carrier

CIF Carrier Indicator Field

CRS Cell Specific Reference Signals

CSG Closed Subscriber Group

DCI Downlink Control Information

HeNB Home eNB

ICIC Inter-Cell Interference Coordination

MBSFN Multi-Media Broadcast over a Single Frequency Network

OFDM Orthogonal Frequency Division Multiple Access

OSG Open Subscriber Group

PBCH Physical Broadcast Channel

PCC Primary Component Carrier

PCFICH Physical Control Format Indicator Channel

PDCCH Physical Downlink Control CHannel

PDSCH Physical Downlink Shared Channel

PHICH Physical Hybrid-ARQ Indicator Channel

PSS Primary Synchronization Channel

PUCCH Physical Uplink Control Channel

PUSCH Physical Uplink Shared Channel

RRC Radio Resource Control

RS Reference Signals

SRS Sounding Reference Signals

SSS Secondary Synchronization Channel

UL DM RS UL Demodulation Reference Signals

DETAILED DESCRIPTION

As explained above, in certain scenarios it is necessary to reduce, oreven set to zero, the transmission power of PSS/SSS and/or PBCH on onecomponent carrier, in order to protect corresponding signals transmittedfrom another node. This is illustrated in FIG. 7, which shows how amacro cell protects PSS/SSS and PBCH from a pico cell by transmittingits corresponding signals with zero/reduced power on carrier f2. If amobile terminal shall be able to connect to the macro cell even close tothe pico cell, e.g. if the pico cell is a CSG cell to which the terminaldoes not have access, then the pico cell has to transmit PSS/SSS andPBCH with zero or reduced power on f1. This means that a mobile terminalmay not be able to derive certain important parameters associated withthe component carrier which is muted. For instance, the cell ID andnumber of TX antenna ports cannot be determined if the PSS/SSS and PBCHcan't be detected. Without knowledge of the cell ID and/or the number ofTX antenna ports corresponding to a given cell, or a given componentcarrier, the mobile terminal cannot determine reference signals,scrambling sequences, etc. for that component carrier, e.g. SCell. Asalready mentioned, the problem is not limited to scenarios where mutingis applied, but may occur whenever the PSS/SSS and/or PBCH cannot bedetected, for instance due to severe interference from a neighboringcell. In all these cases, the end result is that the mobile terminalwill be unable to detect the presence of the cell, perform measurements,and/or establish communication with the cell.

However, even if the mobile terminal is not able to detect thesynchronization and broadcast channels, it may still be possible andbeneficial for the terminal to establish communication with the cell. Asmentioned earlier, synchronization and system information, such asPSS/SSS and PBCH, must be transmitted on certain well-defined resources.This is illustrated in FIG. 8, where a dotted square inside the dataregion schematically illustrates the location of synchronizationchannels. These channels are always transmitted in the same location incells A and B, and if cell A and B use the same carrier frequency,interference will result. However, for data in the data region it ispossible to use ICIC methods to ensure that transmissions do not collidebetween cells A and B. In this example, the frequency resources in thedata region have been partitioned so that cell A uses one part of thedata region, while cell B uses another part, as indicated by the slashedregions in FIG. 8. Thus, the data regions will not interfere with eachother. Provided that a mobile terminal could detect and establishcommunications with both cells A and B, the mobile terminal should haveno problem receiving and/or transmitting data that is comprised in thedata region.

In various embodiments of the present disclosure, the above-mentionedproblem is addressed by transmitting at least one parameter associatedwith a cell, e.g. a secondary cell (SCell), in another cell, e.g. aprimary cell (PCell). In other words, a parameter such as the cell ID ofthe cell, e.g. secondary serving cell (SCell) that is configured on thecarrier frequency, e.g. component carrier which transmits PSS/SSS withreduced or zero power is signaled in another cell. Also, the number oftransmit antenna ports a component carrier is configured with may besignaled in another cell if the PBCH cannot be detected, e.g. because itis transmitted with reduced/zero power. Furthermore, in some scenariosit may be possible to transmit CRS with reduced/zero power—in such casesit is possible to signal this to the terminal, to avoid unspecifiedbehavior in the terminal.

Thus, the mobile terminal receives the required parameters for a cell,e.g. SCell, which are not possible to detect and/or derive from thecell's own transmissions, from another cell, e.g. PCell, which theterminal is able to detect. With knowledge of cell ID and number of TXantenna ports, the mobile terminal is capable of reconstructingreference signals, scrambling sequences, etc. needed for uplink anddownlink operation in the cell, e.g. SCell. Other parameters, such ascarrier frequency, bandwidth and cyclic prefix length indication, mayalso be signaled in the other cell, e.g. PCell. However, in certaincircumstances the mobile terminal may be able to assume default valuesfor some or all parameters; thus, it may not be necessary to signal allthese parameters in the other cell. As an example, a mobile terminal mayassume that the number of antenna ports, bandwidth etc. are the same inthe SCell as in the PCell, if these parameters are not signaled in thePCell.

To perform mobility measurements, a mobile terminal needs to be able toreconstruct the cell-specific reference signals (CRS) and needs to knowthe carrier frequency of the other cell, e.g. SCell (secondary servingcell). Techniques for signaling the carrier frequency of a SCell to amobile have previously been disclosed. For instance, see R2-103427,Change Request CR 0230 to 36.300, “Stage 2 description of CarrierAggregation”, 3GPP TSG-RAN WG2 Meeting #70, Montreal, Canada, 10-14 May2010. Given knowledge of the carrier frequency of the other cell, e.g.SCell, combined with the techniques disclosed herein for signaling thecell ID, a terminal can reconstruct the CRS and thus perform mobilitymeasurements in the other cell, e.g. SCell.

Some deployment scenarios may require that the CRS are transmitted withreduced/zero power in an SCell. In this case, demodulation by the mobileterminal relies on UE-specific reference signals. Even if a terminal isnow capable to reconstruct the CRS it will not measure anythingmeaningful since no CRS are present. To avoid undesirable mobileterminal behavior, e.g., the mobile terminal is configured with asecondary cell SCell, but mobility measurements indicate that this cellis not present, it may be advantageous to signal to the terminal that noCRS are present, or at least they are not detectable, in the SCell. Insuch a case, the mobile terminal may be configured so that it does notprovide any mobility measurements based on CRS on the corresponding cellobject.

Both the cell ID and number of transmit antenna ports are generallystatic parameters, and thus are expected to change only on a very slowbasis. A good signaling choice is therefore to signal cell ID and thenumber of transmit antenna ports of a cell, e.g. SCell, usingsemi-statically signaling, e.g. RRC signaling, in another cell, e.g. theprimary serving cell (PCell) or another SCell.

This signaling is not needed in all scenarios, therefore signaling ofthese values may be enabled on an optional basis. This may be achievede.g. by defining information elements for “Number of TX antenna ports ofSCell” and “Cell ID of SCell” that are optionally included in a messageof the semi-static signaling protocol. The required information may betransmitted to the terminal via dedicated signaling or via broadcast.Accordingly, a terminal configured with at least one secondary cell,SCell, receives required information regarding this secondary cell,SCell, via dedicated signaling or broadcasting. Thus, on top ofpreviously defined system parameters a terminal may optionally receiveadditional parameters defined in this disclosure.

Those skilled in the art will appreciate that cells configured onseparate frequencies may sometimes use the same cell identity. In suchcases, it may be unnecessary to explicitly signal this information tothe mobile terminal, even if it is realized that a mobile terminal needsthis information. Thus, according to one specific embodiment, if aterminal does not receive the newly defined information element “Cell IDof SCell”, then it reuses the cell ID from an already configured cell,either from the primary serving cell PCell or another configuredsecondary cell, e.g. from a second SCell that is used to convey systemparameters for a first SCell. If a terminal, however, receives theinformation element “Cell ID of SCell” it will use this parameter toderive cell ID in the SCell.

This same mechanism is also applicable to the new parameter “Number ofTX antenna ports of SCell”. If a terminal does not receive thisinformation element, it will apply the number of TX antenna ports in theprimary serving cell PCell or another configured secondary cell, e.g.,from a second SCell that is used to convey system parameters for thefirst SCell. If the information element “Number of TX antenna ports ofSCell” is received by the terminal, on the other hand, it will assumethis parameter to derive number of TX antenna ports in the SCell.

If no CRS are transmitted, or if CRS are transmitted with reduced/zeropower, in a secondary cell SCell this may lead to unspecified mobileterminal behavior. To avoid this, the optional information element “CRSnot present in SCell” may be transmitted, in some embodiments. If thisinformation element is received by the terminal it does not assume thepresence of CRS in the secondary cell SCell. If this information elementis not received the terminal assumes CRS are transmitted in thesecondary cell SCell.

A method in a user equipment according to an embodiment will now bedescribed with reference to FIG. 9 and the flowchart in FIG. 10.

FIG. 9 is a schematic drawing illustrating a wireless network 900comprising a macro cell 910 and a pico cell, where the coverage area ofthe pico cell is contained within the coverage area of the macro cell910. The macro cell 910 operates on carrier frequency f2, and is servedby macro base station 940, e.g. an LTE eNB. The pico cell operates oncarrier frequencies, or component carriers, f1 and f2, where f1 is adifferent carrier frequency from f2. Thus, there are actually two cellsconfigured in the pico cell: a first cell 970 configured on componentcarrier f1, and a second cell 980 configured on component carrier f2. Asdescribed above, synchronization signals, reference signals, etc. willbe transmitted in both cells 970 and 980. The pico cell, comprisingcells 970 and 980, is served by pico base station 950, which may forinstance be an LTE home base station, HeNB. A user equipment 920 islocated within the coverage area of both the macro cell 910, and thecells 970 and 980. In this example, the user equipment 920 is a mobileterminal capable of carrier aggregation, e.g. an LTE Release10-compliant UE. The user equipment 920 is initially connected to thefirst cell 970, which is configured on f1; thus, from the point of viewof user equipment 920, the first cell 970 is the primary serving cell,or PCell. It would be advantageous for user equipment 920 to also addthe second cell 980 as a secondary cell (SCell), since this wouldincrease the available bandwidth for the user equipment 920. However,the assumption in this example is that user equipment 920 is not able todetect and/or decode control and synchronization information transmittedover the second cell 980, i.e. the cell configured on carrier frequencyf2. As explained earlier, this problem may occur e.g. because the macrobase station 940 is transmitting at a much higher power on f2, causingso much interference in the cell 980, and in particular on thesynchronization channels PSS/SSS and broadcast channel PBCH, that thesignal from the pico base station 950 on carrier f2 is not detectable.Therefore, user equipment 920 is not able to acquire necessaryparameters, e.g. cell id, for the second cell 980, and it thus cannotadd the second cell as an SCell using standard mechanisms.

According to the method, the user equipment 920 receives, 1010, arequest to add a secondary cell, SCell. The request is received over thefirst cell 970. The request to add the SCell comprises the cell identityof the second cell 980. In some variants, the cell identity is thephysical cell identity of the second cell 980.

In some variants of this embodiment, the request may also comprise otherparameters associated with the second cell 980. For example, one or moreof the parameters carrier frequency, number of transmit antenna ports,bandwidth, or cyclic prefix length indication related to the second cell980 may be received over the first cell 970. However, if the userequipment 920 does not receive one or more of these parameters, the userequipment 920 may assume default values for any parameters that were notreceived. In particular, the user equipment 920 may assume that thenon-received parameters have the same value in the second cell 980 as inthe first cell 970. Therefore, it is not necessary that all parametersassociated with the second cell 980 are received over the first cell970.

In some variants, the user equipment 920 also receives, 1020, anindication over the first cell 970 to use the received parameters, i.e.the cell id and any additional parameters, to derive at least onephysical layer characteristic for the second cell 980. In other words,the indication tells the user equipment 920 that it should derive thephysical layer characteristic from the received parameter, instead oftrying to detect it in the air. An advantage of receiving the indicationis that the user equipment does not need to spend time and resources onunnecessary attempts to decode signals from the second cell 980, whichcould not be successful anyway. However, in other variants the userequipment 920 always uses the received parameters, if present, to derivethe physical layer characteristics. In yet other variants, the userequipment 920 first tries to detect the parameters for the second cell980 over the air, and if this fails it uses the parameters received overthe first cell 970.

It should be noted that the indication may be received in the samemessage as the at least one parameter, or it may be received in aseparate message. The indication may be realized as a flag, e.g. usingone or more unused bits of an existing message. In another alternative,the mere presence of the at least one parameter may be regarded as theindication. Thus, the indication may be implicitly present in themessage. The indication may be received on a broadcast channel in thefirst cell 970.

After having received the cell id and possibly other parameters over thefirst cell 970, the user equipment derives, 1050, at least one physicallayer characteristic for the second cell 980, based on the parameters.The physical layer characteristics may be e.g. scrambling codes,reference signal configurations, or control signaling configurations. Inparticular, the cell identity may be used to derive the cell-specificreference signal configuration, DMRS, SRS, or MBSFN reference signalconfiguration, reference signal hopping pattern, PUSCH hopping pattern,downlink control channel configuration, uplink control channelconfiguration, and scrambling codes for PUSCH, PDSCH, and for L1/L2control signaling. It is pointed out that it is well known in the arthow to derive these characteristics, once the required parameters areknown. Thus, this procedure will not be described in further detail inthis disclosure.

Once the user equipment has derived at least one physical layercharacteristic for the second cell 980, the user equipment 920 adds,1060, a secondary cell corresponding to the received cell identity. Thatis to say, the user equipment 920 adds the second cell 920 as asecondary serving cell, or SCell. It is pointed out that once thenecessary physical layer characteristics of the second cell 980 havebeen derived, the second cell 980 may be added as an SCell using knownprocedures, which will not be described further here.

It is now possible for the user equipment 920 to use the additionalresources provided by the SCell, i.e. the user equipment 920 may receivetransmissions over component carrier f2, i.e. over the second cell 980.The user equipment 920 may additionally perform uplink transmissions onthe uplink carrier which is linked to component carrier f2.

In a variant of this embodiment, the user equipment 920 receives, 1030,over the first cell 970, an indication that no cell-specific referencesignals are detectable in the second cell 980. The user equipment 920may, in response to this indication, refrain from performing anymeasurement on cell-specific reference signals in the second cell, e.g.the user equipment 920 may refrain from mobility measurements based onCRS. This may be advantageous in cases where the CRS are muted, i.e.transmitted with reduced or zero power, in the second cell 980, as anattempt to measure on the undetectable CRS may result in unspecifiedbehavior in the terminal. The same applies in deployments where CRS aretransmitted, but high interference from neighboring cells makes itimpossible to receive the CRS with sufficient good quality.

In a further variant, the user equipment 920 receives, 1040, over thefirst cell 960, information indicating a user-specific reference signalconfiguration associated with the user equipment 920 in the second cell980. This may be beneficial for instance when the cell-specificreference signals cannot be detected. As mentioned above, CRS are moreprone to interference from other cells since they are typicallytransmitted on predefined resources. However, user-specific referencesignals are transmitted in a pattern specific to the user equipment 920,so that they do not collide with reference signals transmitted in othercells. Therefore, it may be more advantageous for the user equipment 920to perform measurements on user-specific reference signals, when theseare available.

Thus, according to this embodiment, the cell identity of the second cell980 is transmitted over the first cell 970. The user equipment may usethis cell id to derive various synchronization-related parametersassociated with the second cell 980. This will enable the user equipment920 to receive transmissions over the second cell 980.

It should be noted that in FIG. 9, cell 980 has been indicated with adashed circle, and drawn slightly smaller than cell 970 for ease ofviewing. This does not necessarily reflect the relation between theactual geographical coverage areas of cells 970 and 980. As the skilledperson will realize, cells 970 and 980 may have the same geographicalcoverage, or cell 970 may be smaller than cell 980, or their coverageareas may differ in various other ways due to e.g. different fadingcharacteristics. Also, the actual coverage areas are not necessarilycircular. It is further pointed out that, although the presentembodiment is described in the context of the scenario of FIG. 9, thedescribed method is applicable in other scenarios as well—for instance,in the scenario of FIG. 4(b), where the user equipment cannot hear amacro cell because of interference from a nearby CSG cell, or in ascenario where transmission on one carrier frequency is muted to protectsignals in another cell, as described above. Thus, cells 970 and 980 mayin other scenarios be served by a macro base station.

Furthermore, cells 970 and 980 are not necessarily served by the samephysical base station. The cells could, for instance, emanate fromdifferent remote radio heads, or they could even be served by twoneighboring base stations, assuming that the coverage areas of cells 970and 980 overlap, and that carrier aggregation across multiple basestations is supported.

It should be noted that although the cell id and any additionalparameters have been described here as being comprised in the request toadd the secondary cell, it is equally possible to receive one or more ofthe parameters in a separate message. Also, one or more of theparameters may be received over a broadcast channel in the first cell970, rather than in a dedicated message to the user equipment 920.

A method in a network node according to an embodiment will now bedescribed, with reference to FIG. 9 and the flowchart in FIG. 11.

The scenario shown in FIG. 9 has already been described in connectionwith the previous embodiment. The present embodiment relates to a methodperformed in the network node 950, which serves the first cell 970configured on carrier frequency f1, and the second cell 980 configuredon carrier frequency f2. A user equipment 920 is connected to the firstcell 970. As mentioned above, network node 950 may be realized as a picoor femto base station, e.g. as an LTE HeNB, but in some alternativescenarios the network node 950 may be a macro base station, such as anLTE eNB.

In this embodiment, the network node 950 serves the second cell 980, andtransmits, 1120, synchronization signals, reference signals or parts ofsystem information over the second cell 980 with reduced or zero power.As explained above, a reason for this muting may be that there isanother nearby cell which is also configured on carrier frequency f2,and which is heavily interfered by transmissions in cell 980. Thus, thenetwork node 950 may mute certain signaling in order to protect anothercell. However, this will also prevent user equipment 920 from detectingthe cell 980.

According to the method, the network node 950 transmits, 1110, a requestto add a secondary cell, SCell. The request is transmitted over thefirst cell 970. The request to add the SCell comprises the cell identityof the second cell 980. In some variants, the cell identity is thephysical cell identity of the second cell 980.

In some variants of this embodiment, the request may also comprise oneor more other parameters associated with the second cell 980, e.g.carrier frequency, number of transmit antenna ports, bandwidth, cyclicprefix length indication.

The network node 950 also transmits, 1110, an indication to use the atleast one parameter to derive at least one physical layer characteristicfor the second cell 980. In other words, the indication tells the userequipment 920 that it should derive the physical layer characteristicfrom the received parameter, instead of trying to detect it in the air.The indication may be transmitted in the same message as the at leastone parameter, or in a separate message. The indication may be realizedas a flag, e.g. using one or more unused bits of an existing message.Alternatively, the indication may be transmitted on a broadcast channelin the first cell 970.

In some further variants, the network node 950 transmits a parameteronly if it has a different value in the second cell 980 than in thefirst cell 970, or if it has a different value than a predetermineddefault value. For example, if the second cell 980 uses the samebandwidth and number of antenna ports as the first cell 970, those twoparameters are not transmitted over the first cell 970. The userequipment 920 may then assume that the non-transmitted parameters havethe same value as in the first cell, or that they have the same value asthe predetermined default value.

In a variant of this embodiment, the network node 950 transmits, 1130,over the first cell 970, an indication that no cell-specific referencesignals are detectable in the second cell 980. The user equipment 920may, in response to this indication, refrain from performing anymeasurement on cell-specific reference signals in the second cell, asdescribed above.

In some further variants, the network node 950 transmits, 1140, over thefirst cell, information indicating a user-specific reference signalconfiguration associated with the user equipment 920 in the second cell980. The user-specific reference signal configuration may be used by theuser equipment 920 as described in the previous embodiment.

By transmitting the necessary parameters over the first cell 970, thenetwork node 950 enables the user equipment 920 to derive physical layercharacteristics that are required to add the second cell 980 as anSCell. Once the user equipment 920 has successfully added the SCell,network node 950 may transmit information to user equipment 920 overcomponent carrier f2, i.e. over the second cell 980.

As already stated in connection with the previous embodiment, thecircles indicating cells 970 and 980 do not necessarily indicate theshape of the actual geographical coverage areas of the cells. It isfurther pointed out that in some scenarios, the network node 950 servesonly the first cell 970, whereas the second cell 980 is served byanother network node. This assumes that carrier aggregation acrossmultiple nodes is supported, and that network node 950 acquires therequired parameters associated with the second cell 980, e.g. from amessage received from the network node which serves the second cell 980.It is also pointed out that, similarly to the previous embodiment, thepresent method is applicable even if muting is not applied in the secondcell 980, since there could be various other reasons why user equipment920 fails to detect the second cell 980.

It should be noted that although the cell id and any additionalparameters have been described here as being comprised in the request toadd the secondary cell, it is equally possible to transmit one or moreof the parameters in a separate message. Also, one or more of theparameters may be transmitted over a broadcast channel in the first cell970, rather than in a dedicated message to the user equipment 920.

A method in a user equipment according to another embodiment will now bedescribed with reference to FIG. 12 and the flowchart in FIG. 13. Thisembodiment relates to mobility measurements performed by a userequipment 1210 in connected mode.

FIG. 12 is a schematic drawing illustrating a wireless network 1200comprising a first cell 1220 and a second cell 1230, with partlyoverlapping coverage areas. The first and second cells both operate onthe same carrier frequency f1. The first cell 1220 is served by networknode 1240, e.g. an LTE eNB. The second cell 1230 is served by networknode 1250, e.g. another LTE eNB. Synchronization signals, referencesignals, etc. will be transmitted in both cells 1220 and 1230. A userequipment 1210 is located within the coverage area of both cells 1220and 1230, and is currently connected to cell 1220. The user equipment1210 is moving in the direction of the arrow 1270. Thus, the userequipment 1210 is getting closer to network node 1250 and it would beadvantageous for the user equipment 1210 to perform mobilitymeasurements on cell 1230, so that a handover decision may eventually bemade. However, in this example the user equipment 1210 is not able todetect and/or decode information transmitted over the second cell 1230.A possible cause of this problem is that network node 1240 istransmitting with a higher power on f1, causing severe interference tothe synchronization channels, broadcast channels, and/or referencesignals in cell 1230. Another possibility is that network node 1250 istransmitting with reduced or zero power on the synchronization and/orbroadcast channels, for instance to protect nearby pico cell 1260 whichis also configured to use carrier frequency f1. Therefore, userequipment 1210 is not able to derive necessary parameters, e.g. cell id,for the second cell 1230, which are needed to receive the cell-specificreference signals, CRS. Consequently, user equipment 1210 cannot performmobility measurements on cell 1230, which may lead to reduced throughputfor user equipment 1210 as it moves further away from network node 1240,and possibly even to a dropped connection if the user equipment 1210moves into the region which is only covered by cell 1230, without beingable to detect the presence of the cell.

According to the method, the user equipment 1210 receives, 1310, arequest to perform measurements on the second cell 1230. The request isreceived over the first cell 1220. The measurement request comprises thecell identity of the second cell 1230. In some variants, the cellidentity is the physical cell identity of the second cell 1230.

In some variants of this embodiment, the request may also comprise otherparameters associated with the second cell 1230. For example, one ormore of the parameters carrier frequency, number of transmit antennaports, bandwidth, cyclic prefix length indication related to the secondcell 1230 may be received over the first cell 1220. The number oftransmit antennas influence the CRS because each antenna port transmitsits own cell-specific reference signals. To be able to reconstruct theCRS the user equipment 1210 needs to know if they are present or not;thus, it needs to know how many antenna ports are used for transmission.However, if the user equipment 1210 does not receive one or more ofthese parameters, the user equipment 1210 may assume default values forany parameters that were not received. In particular, the user equipment1210 may assume that the non-received parameters have the same value inthe second cell 1230 as in the first cell 1220. Therefore, it is notnecessary that all parameters associated with the second cell 1230 arereceived over the first cell 1220.

In some variants, the user equipment 1210 also receives, 1320, anindication over the first cell 1220 to use the received parameters, i.e.the cell id and any additional parameters, to derive at least onephysical layer characteristic for the second cell 1230. In other words,the indication tells the user equipment 1210 that it should derive thephysical layer characteristic from the received parameter, instead oftrying to detect it in the air. An advantage of receiving the indicationis that the user equipment does not need to spend time and resources onunnecessary attempt to decode signals from the second cell 1230, whichcould not be successful anyway. However, in other variants the userequipment 1210 always uses the received parameters, if present, toderive the physical layer characteristics. In yet other variants, theuser equipment 1210 first tries to detect the parameters for the secondcell 1230 over the air, and if this fails it uses the parametersreceived over the first cell 1220.

It should be noted that the indication may be received in the samemessage as the at least one parameter, or it may be received in aseparate message. The indication may be realized as a flag, e.g. usingone or more unused bits of an existing message. In another alternative,the mere presence of the at least one parameter may be regarded as theindication. Thus, the indication may be implicitly present in themessage. The indication may be received on a broadcast channel in thefirst cell 1220.

After having received the cell id and possibly other parameters over thefirst cell 1220, the user equipment 1210 derives, 1330, thecell-specific reference signal configuration for the second cell 1230,based on the parameters. To be able to derive the CRS, the userequipment 1210 may need to derive other physical layer characteristicsas well, e.g. the PBCH scrambling code.

Once the CRS configuration has been determined, the user equipment 1210performs a measurement of the CRS of the second cell 1230 using thederived CRS configuration. In other words, the user equipment 1210performs a mobility measurement on cell 1230.

The user equipment 1210 then transmits a measurement report comprisingthe result of the measurement to its serving network node, i.e. networknode 1240 in this example. The serving network node may use themeasurement report to make a handover decision, possibly handing overthe connection with user equipment 1210 to cell 1230.

In the present example, it has been assumed that user equipment 1210receives the required parameters from its serving cell, i.e. cell 1220.However, it is also possible that the user equipment 1210 is notconnected to the first cell 1220, but to a third cell (not shown in FIG.12). If the parameters for the second cell 1230 are broadcast in thefirst cell 1220, the user equipment 1210 may be able to acquire theparameters even though it is not currently connected to the first cell1220. Any measurement report would then be sent to the serving cell.

It should be noted that although the cell id and any additionalparameters have been described here as being comprised in themeasurement request, it is equally possible to receive one or more ofthe parameters in a separate message. Also, one or more of theparameters may be received over a broadcast channel in the first cell1220, rather than in a dedicated message to the user equipment 1210.

A method in a user equipment according to another embodiment will now bedescribed with reference to FIG. 12 and the flowchart in FIG. 14. Thebasic scenario of FIG. 12 has already been described above, i.e. userequipment 1210 is located in the mutual coverage areas of cells 1220 and1230, and moving in the direction of arrow 1270 away from the coverageof cell 1220. However, in the present embodiment, user equipment 1210 isin idle mode, and it is desirable to perform mobility measurements oncell 1230 for the purpose of a possible cell reselection. As alreadyexplained above, this means that user equipment 1210 needs to measure onthe cell-specific reference signals, CRS, of cell 1230; however, theuser equipment 1210 cannot derive the CRS configuration because ofinterference from cell 1220.

According to the method, the user equipment 1210 receives, 1410, atleast one parameter associated with the second cell 1230. The request isreceived over the first cell 1220. The at least one parameter comprisesthe cell identity of the second cell 1230. In some variants, the cellidentity is the physical cell identity of the second cell 1230.

In some variants of this embodiment, the user equipment 1210 alsoreceives other parameters associated with the second cell 1230. Forexample, one or more of the parameters carrier frequency, number oftransmit antenna ports, bandwidth, cyclic prefix length indicationrelated to the second cell 1230 may be received over the first cell1220. The number of transmit antennas influence the CRS, because eachantenna port transmits its own cell-specific reference signals. To beable to reconstruct the CRS the user equipment 1210 needs to know ifthey are present or not; thus, it needs to know how many antenna portsare used for transmission. However, if the user equipment 1210 does notreceive one or more of these parameters, the user equipment 1210 mayassume default values for any parameters that were not received. Inparticular, the user equipment 1210 may assume that the non-receivedparameters have the same value in the second cell 1230 as in the firstcell 1220. Therefore, it is not necessary that all parameters associatedwith the second cell 1230 are received over the first cell 1220.

In some variants, the user equipment 1210 also receives, 1420, anindication over the first cell 1220 to use the received parameters, i.e.the cell id and any additional parameters, to derive at least onephysical layer characteristic for the second cell 1230. In yet othervariants, the user equipment 1210 first tries to detect the parametersfor the second cell 1230 over the air, and if this fails it uses theparameters received over the first cell 1220. It should be noted thatthe indication may be received in the same message as the at least oneparameter, or it may be received in a separate message. The indicationmay be realized as a flag, e.g. using one or more unused bits of anexisting message. In another alternative, the mere presence of the atleast one parameter may be regarded as the indication. Thus, theindication may be implicitly present in the message.

Note that in this embodiment, the one or more parameters, and theindication, are all received on a broadcast channel in the first cell1220, since the user equipment 1210 is in idle mode.

After having received the cell id and possibly other parameters over thefirst cell 1220, the user equipment 1210 derives, 1430, thecell-specific reference signal configuration for the second cell 1230,based on the parameters. To be able to derive the CRS, the userequipment 1210 may need to derive other physical layer characteristicsas well, e.g. the PBCH scrambling code.

Once the CRS configuration has been determined, the user equipment 1210performs a measurement, 1440, on the CRS of the second cell 1230 usingthe derived CRS configuration. In other words, the user equipment 1210performs a mobility measurement on cell 1230.

Depending on the result of the measurement, the user equipment 1210 maydecide to initiate a cell reselection procedure, according to knownmechanisms.

A method in a network node according to another embodiment will now bedescribed with reference to FIG. 12 and the flowchart in FIG. 15. Here,a scenario is described where network node 1240 requests user equipment1210 to perform mobility measurements on cell 1230; thus, the embodimentis similar to the one described in connection with FIG. 13 above, buthere the focus is on a method performed in the network node 1240.

According to the method, the network node 1240 transmits, 1510, arequest to the user equipment 1210 to perform measurements on the secondcell 1230. The request is transmitted over the first cell 1220. Themeasurement request comprises the cell identity of the second cell 1230.In some variants, the cell identity is the physical cell identity of thesecond cell 1230.

In some variants of this embodiment, the request may also comprise otherparameters associated with the second cell 1230. For example, one ormore of the parameters carrier frequency, number of transmit antennaports, bandwidth, cyclic prefix length indication related to the secondcell 1230 may be transmitted over the first cell 1220. The number oftransmit antennas influence the CRS because each antenna port transmitsits own cell-specific reference signals. To be able to reconstruct theCRS the user equipment 1210 needs to know if they are present or not;thus, it needs to know how many antenna ports are used for transmission.

The network node 1240 also transmits, 1510, an indication to use the atleast one parameter to derive at least one physical layer characteristicfor the second cell 1230. In other words, the indication tells the userequipment 1210 that it should derive the physical layer characteristicfrom the received parameter, instead of trying to detect it in the air.The indication may be transmitted in the same message as the at leastone parameter, or in a separate message. The indication may be realizedas a flag, e.g. using one or more unused bits of an existing message.Alternatively, the indication may be transmitted on a broadcast channelin the first cell 1220. In another alternative, the mere presence of theat least one parameter may be regarded as the indication. Thus, theindication may be implicitly present in the message.

By transmitting the parameters and indication over the first cell 1220,the network node 1240 enables the user equipment 1210 to derive thenecessary physical layer characteristics for the second cell 1230. Thiswill allow the user equipment 1210 to perform the requested measurementseven it could not initially detect cell 1230.

The network node 1240 then receives, 1530, a measurement report fromuser equipment 1210. Network node 1240 may use the measurement report tomake a handover decision, possibly handing over the connection with userequipment 1210 to cell 1230.

In some variants of this embodiment, the network node 1240 serves thesecond cell 1230, and transmits, 1520, synchronization signals,reference signals or parts of system information over the second cell1230 with reduced or zero power. As explained above, a reason for thismuting may be that there is another nearby cell which is also configuredon carrier frequency f1, and which is heavily interfered bytransmissions in cell 1230. Thus, the network node 1240 may mute certainsignaling in order to protect pico cell 1260. However, this may alsoprevent user equipment 1210 from detecting the cell 1230. It should benoted, however, that the method is also applicable when muting is notused, since there are various other reasons that could prevent userequipment 1210 from detecting signals in cell 1230.

It should be noted that although the cell id and any additionalparameters have been described here as being comprised in themeasurement request, it is equally possible to transmit one or more ofthe parameters in a separate message. Also, one or more of theparameters may be transmitted over a broadcast channel in the first cell1220, rather than in a dedicated message to the user equipment 1210.

A general method performed in a user equipment according to severalembodiments will now be described with reference to the flow chart ofFIG. 16.

The user equipment receives, 1610, over a first cell configured on acarrier frequency, at least one parameter associated with a second cellconfigured on a carrier frequency. The at least one parameter comprisesa cell identity.

As mentioned in the specific embodiments discussed above, the first andsecond cells may be configured on the same, or different, carrierfrequencies. In some embodiments, the first cell is the PCell of theuser equipment.

In some embodiments, the user equipment also receives, 1620, over thefirst cell, an indication to use the at least one parameter to derive atleast one physical characteristic for the second cell.

In some embodiments, the user equipment also receives, 1630, over thefirst cell, an indication that no CRS are detectable in the second cell.

In some further embodiments, the user equipment receives, 1640, anindication of a user-specific reference signal configuration over thefirst cell.

The user equipment then derives, 1650, at least one physical layercharacteristic for the second cell based on the received at least oneparameter, thereby enabling the user equipment to receive transmissionsover the second cell. In some embodiments, the user equipment mayproceed to add the second cell as an SCell. In other embodiments, theuser equipment may derive a CRS configuration for the second cell, anduse this to perform mobility measurements in idle mode or connectedmode.

A general method performed in a network node according to severalembodiments will now be described with reference to the flow chart ofFIG. 17. The network node serves a first cell configured on a carrierfrequency.

According to the method, the network node transmits, 1710, over thefirst cell, at least one parameter associated with a second cellconfigured on a carrier frequency. The at least one parameter comprisesa cell identity. The network node also transmits an indication to usethe at least one parameter to derive at least one physical layercharacteristic for the second cell. The cell identity and possible otherparameters may be comprised in a measurement request message sent to auser equipment, or they may be included in a request to add the secondcell as an SCell.

In some embodiments, the network node serves also the second cell, andtransmits synchronization signals, reference signals, or part of systeminformation over the second cell with reduced or zero power.

In some embodiments, the network node also transmits, 1730, over thefirst cell, an indication that no CRS are detectable in the second cell.

In some further embodiments, the network node transmits, 1740, anindication of a user-specific reference signal configuration over thefirst cell.

FIGS. 18 and 19 illustrate example implementations of user equipment920, 1110, and network node 940, 1140. It is pointed out that thesedevices may include computer-based circuitry, such as one or morecircuits based on microprocessors, digital signal processors, ASICs,FPGAs, or other programmable or programmed digital processing circuitry.The operation of these devices may be implemented in whole or in part byconfiguring the device via the execution of stored computer programs,held in memory or other computer-readable media to which the device hasaccess. Thus, it should be appreciated that the processing circuitsillustrated in FIGS. 18 and 19 may be implemented in hardware, software,or a combination of both.

FIG. 18 illustrates a user equipment 1800, comprising a transceiver 1810and one or more processing circuits 1820. The processing circuits 1820are configured to receive, over a first cell 970 configured on a carrierfrequency, at least one parameter associated with a second cell 980configured on a carrier frequency. The at least one parameter comprisesa cell identity. The processing circuits 1820 are further configured toderive at least one physical layer characteristic for the second cell980 based on the received at least one parameter, thereby enabling theuser equipment 920 to receive transmissions over the second cell 980.The at least one parameter may further comprise one or more of: carrierfrequency, number of transmit antenna ports, bandwidth, cyclic prefixlength indication.

In some variants, the processing circuits 1820 are further configured toreceive, over the first cell 970, an indication that the user equipment920 should use the received at least one parameter to derive at leastone physical layer characteristic for the second cell 980. The at leastone physical layer characteristic may comprise one or more of: a PUSCH,PDSCH, L1/L2 control signaling or CRC of PBCH scrambling code, acell-specific reference signal configuration, a sounding referencesignal configuration, an MBSFN reference signal configuration, an uplinkdemodulation reference signal configuration, a downlink or uplinkcontrol signaling configuration, a reference signal hopping pattern, ora PUSCH hopping pattern.

In some further variants, the processing circuits 1820 are furtherconfigured to receive, over the first cell 970, an indication that nocell-specific reference signals are detectable in the second cell 980.The processing circuits 1820 may be further configured to, in responseto the indication that no cell-specific reference signals aredetectable, not attempt to perform any measurement on cell-specificreference signals in the second cell 980.

In some variants, the processing circuits 1820 are further configured toreceive, over the first cell 970, information indicating a user-specificreference signal configuration associated with the user equipment 920 inthe second cell 980.

In some variants, the processing circuits 1820 are further configured toreceive the at least one parameter over a broadcast channel.

In some other variants, the processing circuits 1820 are configured toreceive the at least one parameter in a measurement request. Theprocessing circuits 1820 may be further configured to detect the secondcell (980) by means of the cell identity received in the measurementrequest message. The processing circuits 1820 may be further configuredto perform a measurement of a signal, e.g. a cell-specific referencesignal, received over the second cell 980, by means of a receivedreference signal configuration, and to transmit a measurement report.

In some other variants, the processing circuits 1820 are configured toreceive the at least one parameter in a request to add a secondary cell.The processing circuits 1820 may be further configured to add asecondary cell corresponding to the received cell identity.

In some variants, the processing circuits 1820 are configured to assumethat, if the user equipment 920 does not receive one or more of theparameters carrier frequency, number of transmit antenna ports,bandwidth, or cyclic prefix length indication, the parameters notreceived have the same value in the second cell 980 as in the first cell970.

The user equipment 1800 may comprise more than one transceiver.

FIG. 19 illustrates a network node 1900, comprising a transceiver 1910and one or more processing circuits 1920. The processing circuits 1920are configured to transmit, over a first cell 970 configured on acarrier frequency, at least one parameter associated with a second cell980 configured on a carrier frequency, wherein the at least oneparameter comprises a cell identity. The processing circuits 1920 arefurther configured to transmit an indication to use the at least oneparameter to derive at least one physical layer characteristic for thesecond cell 980. The at least one parameter may further comprise one ormore of: carrier frequency, number of transmit antenna ports, bandwidth,cyclic prefix length indication.

In some variants, the processing circuits 1920 are further configured totransmit synchronization signals, reference signals or parts of systeminformation over the second cell 980 with reduced or zero power;

In some variants, the processing circuits 1920 are further configured totransmit, over the first cell 970, an indication that no cell-specificreference signals are detectable in the second cell 980.

In some variants, the processing circuits 1920 are further configured totransmit, over the first cell 970, information indicating auser-specific reference signal configuration associated with a userequipment 920 in the second cell 980.

In some variants, the processing circuits 1920 are further configured toperform the transmissions over a broadcast channel.

In some other variants, the processing circuits 1920 are furtherconfigured to perform the transmissions in a dedicated message to a userequipment 920, e.g. a measurement request or a request to add asecondary cell.

In some variants, the processing circuits 1920 are further configured totransmit a parameter only if it has a different value in the second cell980 than in the first cell 970.

The network node 1900 may comprise more than one transceiver.

The solutions described above have been detailed in connection withcarrier aggregation and heterogeneous networks, as specified for LTEnetworks. However, those skilled in the art will appreciate that thetechniques and concepts described herein are more generally applicableto other wireless communication systems, where interference prevents amobile terminal from detecting and/or communicating with a cell.Particular embodiments disclosed herein address carrier aggregationand/or the layered use of primary and secondary cells, i.e.heterogeneous systems in general. Thus, the present disclosure is notlimited to LTE implementations.

Some embodiments disclosed herein enable acquisition of cell ID of acell configured on a component carrier and, optionally, number oftransmit antenna ports, carrier frequency, bandwidth, cyclic prefixlength indication for a component carrier on which PSS/SSS and PBCH aretransmitted with reduced/zero power or received with bad quality due tohigh interference. This is needed in carrier aggregation basedheterogeneous network deployments.

Those skilled in the art will further appreciate that the variousmethods and processes described herein may be implemented using varioushardware configurations, generally, but not necessarily including theuse of one or more microprocessors, microcontrollers, digital signalprocessors, or the like, coupled to memory storing software instructionsfor carrying out the techniques described herein. As the design and costtradeoffs for the various hardware approaches, which may depend onsystem-level requirements that are outside the scope of the presentdisclosure, are well known to those of ordinary skill in the art,further details of specific hardware implementations are not providedherein.

Various embodiments of the techniques and concepts include radio basestations, such as LTE eNBs, comprising processing circuits configured tocarry out the processes discussed above. Other embodiments includemobile terminals comprising processing circuits configured to carry outprocesses complementary to those performed by the base stations, plus,in some cases, additional processes.

Thus, the present disclosure is not limited to the above-describedpreferred embodiments. Various alternatives, modifications andequivalents may be used. Therefore, the above embodiments should not betaken as limiting the scope of the disclosure, which is defined by theappending claims.

When the word “comprise” or “comprising” is used in this disclosure, itis intended to be interpreted as non-limiting, i.e. meaning “consist atleast of”.

What is claimed is:
 1. A method in a user equipment, the methodcomprising: configuring the user equipment to receive transmissions overa second cell configured on a carrier frequency based on a physicallayer characteristic for the second cell, wherein the physical layercharacteristic is derived from one or more parameters received over afirst cell configured on a carrier frequency; receiving thetransmissions over the second cell; receiving, over the first cell, anindication that no cell-specific reference signals are detectable in thesecond cell; and in response to the indication that no cell-specificreference signals are detectable, the user equipment does not attempt toperform any measurement on cell-specific reference signals in the secondcell.
 2. The method of claim 1 wherein the one or more parameterscomprise information indicating a cell identity of the second cell, anda number of transmit antenna ports at the second cell.
 3. The method ofclaim 1 further comprising receiving, over the first cell, an indicationthat the user equipment should use the one or more parameters receivedover a first cell to derive the at least one physical layercharacteristic for the second cell.
 4. The method of claim 1 wherein theat least one physical layer characteristic comprises one or more of: ascrambling code, a reference signal configuration, a control signalingconfiguration.
 5. The method of claim 4 wherein the at least onephysical layer characteristic comprises one or more of: a PUSCHscrambling code, a PDSCH scrambling code, a L1/L2 control signalingscrambling code.
 6. The method of claim 4 wherein the at least onephysical layer characteristic comprises one or more of: a cell-specificreference signal configuration, a sounding reference signalconfiguration, an MBSFN reference signal configuration, an uplinkdemodulation reference signal configuration, a reference signal hoppingpattern, a PUSCH hopping pattern, a downlink control channelconfiguration, an uplink control channel configuration.
 7. The method ofclaim 1 wherein the one or more parameters further comprise one or moreof: the carrier frequency, a number of transmit antenna ports, abandwidth, and a cyclic prefix length indication.
 8. The method of claim1 wherein the at least one physical layer characteristic comprises areference signal configuration, the method further comprising:performing a measurement of a signal received over the second cell basedon the reference signal configuration; and transmitting a measurementreport.
 9. The method of claim 2 wherein the cell identity is includedin a request to add a secondary cell.
 10. The method of claim 9 furthercomprising adding the second cell corresponding to the received cellidentity.
 11. The method of claim 1 wherein the first cell is configuredon the same carrier frequency as the second cell.
 12. The method ofclaim 1 wherein if the one or more parameters received at the userequipment does not include the carrier frequency, a number of transmitantenna ports, a bandwidth, or a cyclic prefix length indication, theuser equipment assumes that the parameters not received have a samevalue in the second cell as in the first cell.
 13. A method in a networknode, the network node serving a first cell configured on a carrierfrequency, the method comprising: configuring user equipment to receivetransmissions over a second cell configured on a carrier frequency,wherein configuring the user equipment comprises: transmitting one ormore parameters associated with the second cell to the user equipmentover the first cell, wherein for each of the one or more parameters, thenetwork node transmits the parameter only if the parameter has adifferent value in the second cell than in the first cell; andindicating to the user equipment to derive at least one physical layercharacteristic for the second cell based on the one or more parameters.14. The method of claim 13 wherein the one or more parameters comprise acell identity of the second cell and a number of transmit antenna ports.15. The method of claim 13 wherein the network node serves the secondcell, the method further comprising transmitting synchronizationsignals, reference signals or parts of system information over thesecond cell with reduced or zero power.
 16. The method of claim 13further comprising transmitting, over the first cell, an indication thatno cell-specific reference signals are detectable in the second cell.17. A mobile terminal comprising: processing circuitry configured to:configure the mobile terminal to receive transmissions over a secondcell configured on a carrier frequency based on a physical layercharacteristic for the second cell, wherein the physical layercharacteristic is derived from one or more parameters received over afirst cell configured on a carrier frequency; receive, over the firstcell, an indication that no cell-specific reference signals aredetectable in the second cell; and in response to the indication that nocell-specific reference signals are detectable, not attempt to performany measurement on cell-specific reference signals in the second cell;and a transceiver configured to receive the transmissions over thesecond cell.
 18. A network node comprising: processing circuitryoperative to: configure a mobile terminal to receive transmissions overa second cell configured on a carrier frequency based on a physicallayer characteristic for the second cell, wherein the physical layercharacteristic is derived from one or more parameters sent to the userequipment over a first cell configured on a carrier frequency; and atransceiver configured to transmit: the one or more parameters to mobileterminal over the first cell, wherein for each of the one or moreparameters, the transceiver transmits the parameter only if theparameter has a different value in the second cell than in the firstcell; and an indication to the mobile terminal to derive the physicallayer characteristic for the second cell based on the one or moreparameters.